• Korean Journal of Environmental Biology
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• v.31 no.2
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• pp.113-120
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• 2013

This study aimed to investigate the effects of ultrasonic wave on colonial changes of Microcystis sp. causing water-bloom. The effects of frequency change and exposure time of ultrasonic wave on Microcystis sp. were also perceived by measuring the concentration of chlorophyll-a. The concentrations of chlorophyll-a showed a decreasing tendency in all experimental groups exposed to ultrasonic waves, especially the highest decrease at 70 kHz. Before exposed to ultrasonic wave, single cells of Microcystis sp. were observed in a form of colonies which were densely accumulated onto their mucilage layer. However, after one hour exposure to 70 kHz ultrasonic wave, the bonds of colonies were weakened and single cells were separated from the colonies. Moreover, the single cells of the colony were destroyed with the 5 hour exposure time at 70 kHz. As a result, we proposed that the frequency strength and the exposure time of ultrasonic wave might have effects in decrease of biomass of blue-green algae by reducing the concentration of chlorophyll-a, thereby changing and destroying forms of Microcystis sp. colonies.

• Ecology and Resilient Infrastructure
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• v.8 no.3
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• pp.143-153
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• 2021

The growth inhibition effects of M. aeruginosa were verified using large volume (7.2 L) of algae samples and ultrasonication (high frequency of 1.6 MHz vs. low frequency of 23 kHz) in lab-scale experiment. The chlorophyll-a (chl-a) and cell number decreased gradually after 6 hr sonication with high frequency of 1.6 MHz whereas both decreased sharply after 6 hr sonication with low frequency of 23 kHz. Additionally, the first order degradation coefficient (k) values after sonication were greater than those during sonication. These results indicate that relatively low sonication energy per volume may affect the cell membrane and internal organs of M. aeruginosa in a slow and retarded manner and resulted in gradual decrease of cell numbers of M. aeruginosa. Based on the comparison of chl-a and cell number of M. aeruginosa after sonication, low frequency of 23 kHz is superior for growth inhibition of M. aeruginosa, since low frequency of 23 kHz easily penetrates the cell membrane and ruptures the internal organs including gas vesicles. As is evident in SEM and TEM images, ruptured cell membranes were clearly observed for low frequency of 23 kHz. Finally, the microcystin-LR in water is not detected and considered to be harmless in aquaculture systems.

• The Journal of the Acoustical Society of Korea
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• v.38 no.4
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• pp.459-466
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• 2019

When a laser pulse is irradiated on a CNT (Carbon Nanotube) and PDMS (Poly dimethylsiloxane) composite coated on a transparent PMMA (Poly methyl methacrylate) substrate, a strong ultrasonic wave is generated due to the thermoelastic effect. In this paper, the thermoacoustic theory related to the wave generation by the CNT/PDMS composite was established. The waveforms of ultrasonic waves when a laser pulse having a Gaussian waveform is irradiated on the composite with a thickness of $20{\mu}m$ were numerically simulated. From the results, it was confirmed that ultrasonic shock waves can be generated from the CNT/PDMS composite and the waveforms are changed little even if the physical properties of the composite are changed by ${\pm}20%$. It was found that the peak positive and negative pressures increase as the thermal expansion coefficient increases, or as density, heat capacity and sound speed decreased. However, those changes were not so sensitive with thermal conductivity. In addition, the physical properties of the CNT/PDMS composite fabricated in this study were estimated from the comparison of the measurement and simulation results.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.05a
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• pp.341-344
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• 2003

There communicates using tire supersonic waves in tire underwater, that is different from tire ground that use tire propagation. Because using Law frequency to come under tire waves, bandwidth that is able to communicate is very smaller that tire mobile communication of tire ground. Also, The channel environment changes rapidly in tire shallow underwater than tire ground. Due to such a reason, data transmission technic that is able to tire maximum application to restricted bandwidth and tire signal processing technics that is able to conquer tire rapid changes of tire channel environment are being used. Algorithm is used at tire application of these technic has a lot of tire calculating quantity. So this research reveals small bulk and equal performance using one DSP chip and then implements QPSK transmitter, that uses SHARC DSP of Analog Device company, for tire underwater supersonic waves communication rapidly decrease tire calculating quantity.

• Journal of Ocean Engineering and Technology
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• v.19 no.5 s.66
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• pp.71-77
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• 2005

This paper presents an integrated underwater navigational algorithm for unmanned underwater vehicles, using additional two-range transducers. This paper proposes a measurement model, using two range measurements, to improve the performance of an IMU-DVL (inertial measurement unit - Doppler velocity log) navigation system for long-time operation of underwater vehicles, excluding DVL measurement. Extended Kalman filter was adopted to propagate the error covariance, to update the measurement errors, and to correct the state equation when the external measurements are available. Simulation was conducted with the 6-d.o.f nonlinear numerical model of an AUV in lawn-mowing survey mode, at current flaw, where the velocity information is unavailable. Simulations illustrate the effectiveness of the integrated navigation system, assisted by the additional range measurements without DVL sensing.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.48 no.6
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• pp.91-98
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• 2011

This paper proposes an efficient and accurate vision based recognition and tracking framework for texture free objects. We approached this problem with a two phased algorithm: detection phase and tracking phase. In the detection phase, the algorithm extracts shape context descriptors that used for classifying objects into predetermined interesting targets. Later on, the matching result is further refined by a minimization technique. In the tracking phase, we resorted to meanshift tracking algorithm based on Bhattacharyya coefficient measurement. In summary, the contributions of our methods for the underwater robot vision are four folds: 1) Our method can deal with camera motion and scale changes of objects in underwater environment; 2) It is inexpensive vision based recognition algorithm; 3) The advantage of shape based method compared to a distinct feature point based method (SIFT) in the underwater environment with possible turbidity variation; 4) We made a quantitative comparison of our method with a few other well-known methods. The result is quite promising for the map based underwater SLAM task which is the goal of our research.

• Journal of the Korean Chemical Society
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• v.50 no.6
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• pp.454-463
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• 2006

refractory organic compounds in aqueous solution are not readily removed by the existing conventional wastewater treatment process. In recent years, the sonolysis and electrochemical oxidation process had been shown to be promising for wastewater treatment due to the effectiveness and easiness in operation. This study was performed to investigate the characteristics of sonolytic and electrolytic decomposition as the basic data for development of the wastewater treatment process. Trichloroethylene(TCE) and 2,4- dichlorophenol(2,4-DCP) were used as the samples, and their destruction efficiency were measured with various operating parameters, such as initial solution concentration, initial solution pH, reaction temperature, sonic power and current density. Also, the decomposition mechanism conformed indirectly with the effect of NaHCO3 as a radical scavenger on the decomposition reaction. Thermal decompositon reaction is predominant for TCE but thermal and radical decompositon reactions were dominant for 2,4-DCP. Results showed that the destruction efficiencies of all samples were above 65% within 120 minutes by sonolysis and electrolysis at the same time, and were increased with increasing initial concentration, sonic power and current density. Destruction efficiency of TCE was high in the acidic solution, but 2,4-DCP showed high destruction efficiency in basic solution.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2000.05a
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• pp.410-418
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• 2000

In general, the experienced diver go into the water to find out Pan Shell which is spontaneously generated and brought up at the depth of 25-30 meters in the slime along the bank of an inlet of western and southern sea. However, this searching system has caused some problems in terms of economical efficiency and riskiness of diver. To overcome such problems and enhance the competence capability of fishermen, a new Pan Shell searching system is required. If an onboard searching system as a substitute of the way of diving into the deep water to identify the existence of Pan Shell is developed, it would be greatly beneficial to fishermen. The purpose of this research is to develop a new searching system of Pan Shell by making use of 50-200 Khz Ultra Sonic Signal, A/D Converter and computer process program. Based on the fact that Sonic Signal between the soft part of slime and the hard part of sand, pebble and Pan Shell is different, the possibility of this system have been approved in some degree by this time of research. However, to utilize this new system, further research on the establishment of data base and sample data is required. With the theoretical knowledge, the systematic research on the searching capability of Ultra Sonic Signal will be continued to identify the influence against the sea water subject. In this research, signal will be analyzed according to the influence range, power and sensitiveness of Ultra Sonic Generator. In addition, the radius of Ultra Sonic Signal will be included. The experimental field work will be executed at Nockdong, Pulkyo and other places well known as a habitat of Pan Shell.

• The Journal of the Acoustical Society of Korea
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• v.20 no.6
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• pp.57-65
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• 2001

In this paper, we designed the acoustic horn for magnetostrictive ultrasonic transducers in a theoretical manner, and validity of the analysis was verified through comparison with the results of finite element analysis. Results of the two analysis methods showed good agreement with each other. The theoretical method can fairly quickly determine the horn length that satisfies given frequency specification, but also has the drawback that it is applicable only to the frequency range over the cut-off frequency. According to the results, the catenoidal horn can provide larger amplification than the exponential horn. It was also found that it is more desirable for the region having the catenoidal curvature to be as short as possible to achieve larger amplification of the transducer deformation. Based on the analysis results, a magneto-strictive transducer sample was fabricated and its performance was evaluated experimentally. The transducer has the resonance frequency of 19.3 ㎑ as well as the maximum SPL of 199 dB, and shows the omni-directional radiation pattern.

• The Journal of the Acoustical Society of Korea
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• v.29 no.6
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• pp.388-394
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• 2010

In the present study, polyacetal bone mimics with circular cylindrical pores were used to investigate variations of speed of sound and attenuation coefficient with porosity and microarchitecture in bone. The speed of sound and attenuation coefficient of the 6 bone mimics with porosities from 0 % to 65.9 % were measured by a through-transmission method in water, using a pair of broadband, unfocused transducers with a diameter of 12.7 mm and a center frequency of 1.0 MHz. Independently of the structural properties of the bone mimics, the speed of sound decreased almost linearly with the increasing porosity. The attenuation coefficient measured at 1.0 MHz exhibited linear or nonlinear correlations with the porosity, depending on the structural properties of the bone mimics. These results are consistent with those previously published by other researchers using bone samples and mimics, and advances our understanding of the relationships of the ultrasonic parameters for the diagnosis of osteoporosis with the bone density and microarchitecture in human bones.